Significant Reduction in Stratospheric Ozone Deficit:
a 3-D Model Study Using UARS Data

Rashid Khosravi

National Center for Atmospheric Research
Laboratory for Atmospheric and Space University of Colorado

Guy P. Brasseur

Anne Smith
National Center for Atmospheric Research

David W. Rusch

Laboratory for Atmospheric and Space Physics, University of Colorado

Joe W. Waters

Jet Propulsion Laboratory, California Institute of Technology

James M. Russell III

Hampton University

ABSTRACT

We present a near global analysis of the ozone deficit problem using, co-located UARS measurements of (MLS) ClO, and (HALOE) NOx, H2O, and CH4 in a fully time dependent, 3-D, chemical, radiative, transport model of the middle atmosphere.  The domain of the study covers a wide range of altitudes (37.4 to 49.6 km) and latitudes (62.5oS to 27.5oN), for the period of January/March 1992.  In this domain, the baseline (no constraints with measurements), model temperatures are mostly warmer than the UKMO observations (by up to 5 K), and [O3] is underestimated by 10 to 25% relative to HALOE measurements.  Also, in this domain, the model/data discrepancies in concentrations of the ozone relevant species, when the model temperature is constrained, are as follows: [H2O] and [NOx] are mostly in good agreement, [CH4] is underestimated by 10-60%, and [ClO] is overestimated by 1.3 to 3 times.

We find the following:

1. Constraining the model with UKMO temperatures eliminates about 3-10% of the deficit in the 40-48 km altitude range

2. Constraining the model with the observed NOx or H2O (in addition to temperature) has minimal effect in most parts of the domain

3. When the model temperatures and ClO profiles are constrained with observations, the deficit is reduced to about 5-15%, bringing model ozone predictions in the 40 km region to within the uncertainties in HALOE ozone measurements

4. a 40% reduction in the rate constant of HO2 + O -> OH + O2, in addition to constraining T, NOx, and ClO, eliminated the deficit in portions of the 40 km region and in the upper stratosphere, but results in 5-10% excess ozone near the equatorial stratopause

5. When the model methane profile is constrained with HALOE observations, and a 6% HCl + O2 channel for the ClO + OH reaction is included in the chemistry, the model ClO abundance agrees well with the MLS measurements in most parts of the domain.  Further improvement in the ClO abundance can be obtained by decreasing [OH] through reducing the rate constant of the HO2 + O -> OH + O2 reaction.